This invention relates in general to hemodialysis. It relates, more particularly, to hemodialysis catheters.
Hemodialysis, as practiced today, normally employs one of two types of hemodialysis catheter to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a tube containing two lumens is used, each lumen having a generally semi-cylindrical or D-shape configuration. This type of catheter is frequently referred to as a dual lumen catheter. Alternatively, two separate tubes, each with a full cylindrical configuration, are used to remove blood for dialysis and return the processed blood.
Flow rates possible with conventional dual lumen catheters are usually lower than those achievable where separate tubular lumens are used to remove blood from a vein for dialysis and then return processed blood back to the vein. Thus, two tube lumens have become more and more popular as the capacity (maximum flow rate) of hemodialysis membranes has increased.
Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein (the venous line) and the line removing blood for purification (the arterial or intake line) at flow rates above 300 ml per minute. A high flow rate from the venous line can cause whipping or xe2x80x9cfirehosingxe2x80x9d of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line causes the port to be sucked into the vein wall, resulting in occlusion. It should be understood, of course, that both lines normally access the superior vena cava and the designations are used for differentiation purposes.
Speed of flow through a catheter lumen, whether it be in a single lumen or a dual lumen catheter, is controlled by a number of factors including the smoothness of the wall surface, the internal diameter or cross-sectional area of the tube lumen, and the length of the tube lumen. The most important factor is the cross-sectional area of the tube lumen. The force or speed of the fluid flow in a tube lumen for a given cross-sectional area is controlled by the external pumping force, of course. This is a positive pressure pushing processed blood through the venous lumen and a negative (suction) pressure pulling unprocessed blood through the arterial lumen.
Problems encountered in providing for a high flow rate through a catheter are magnified in a dual lumen catheter construction. Because each of the lumens in a dual lumen catheter has a D-shape, it has been assumed that flow rates are limited. Furthermore, such dual lumen catheters are, to a great extent, catheters with a main port, which opens at the end of a lumen substantially on the axis of the lumen. Thus, firehosing frequently results. There are dual lumen catheters which utilize side ports for both outflow and inflow. An example is the catheter disclosed in the Cruz et al. U.S. Pat. No. 5,571,093. However, such catheters have not been successful in solving numerous problems related to hemodialysis with dual lumen catheters, e.g., high incidences of catheter port occlusion as well as some degree of fire-hosing still occurs.
An object of the present invention is to provide an improved hemodialysis catheter.
Another object is to provide an improved dual lumen hemodialysis catheter.
Another object is to provide a dual lumen hemodialysis catheter which accommodates flow rates substantially as high as the latest separate lumen catheters.
Still another object is to provide a dual lumen hemodialysis catheter which is capable of returning processed blood to the patient at high flow rates without harmful firehosing of the catheter tip.
Yet another object is to provide a dual lumen hemodialysis catheter which permits high flow rates while minimizing trauma and potential red cell damage so as to substantially avoid clotting.
A further object is to provide a dual lumen hemodialysis catheter which substantially reduces the incidence of port occlusion.
Still a further object is to provide a dual lumen hemodialysis catheter in which occlusion of the return line port is substantially avoided regardless of the flow rate.
Yet a further object is to provide a new and improved bolus design and construction in a dual lumen hemodialysis catheter.
The foregoing and other objects are realized in accord with the present invention by providing a hemodialysis catheter including a dual lumen catheter tube, a bullet-nose bolus having a radially extending main outflow or venous port, at least one additional outflow or venous port radially extending through either the bolus or the tube and at least one intake or arterial port radially extending through the bolus or the tube. An additional outflow port is circumferentially displaced 180xc2x0 around the tube from the main outflow port, and axially displaced from the main outflow port. A main intake port is circumferentially displaced 180xc2x0 around the tube from the additional outflow port. The use of such bolus, port and dual lumen tube combinations produces high flow rates, maximum diffusion, minimum occlusion and minimum vein wall damage in a dual lumen hemodialysis catheter.
In a first embodiment of the invention, the arterial and the venous lumens open through a radially extending main venous port and an intake or arterial port which are immediately adjacent each other on one side of the bolus next to the bullet nose in the bolus. The venous lumen also opens through a second outflow port formed in the tube adjacent the bolus and circumferentially displaced 180xc2x0 around the axis of the catheter tube from the main venous port. Directly opposite this second venous port, the tube body wall is thickened in an oval pattern to form a longitudinally elongated bulge. The bulge forms a stiffening arch in the tube wall and prevents buckling of the tube at the second venous or outflow port.
In a second embodiment of the invention, the venous and arterial lumens open through radially extending, axially displaced main outflow and intake ports on the same side of the catheter bolus. A main outflow port for the venous lumen port is formed radially in the bolus adjacent its bullet nose. A second outflow port for the venous lumen is formed radially in the bolus, circumferentially removed 180xc2x0 from the main port, and displaced axially from the main port. A third outflow port is formed radially in the bolus, axially aligned with the main outflow port and axially displaced from both the main and second outflow ports. A main inflow or arterial port is formed radially in the bolus at a point axially displaced in the bolus from the outflow ports.
In the second embodiment, directly opposite each of the second and third outflow ports and the main intake port, the tube body wall is thickened in an oval pattern to form a longitudinally elongated bulge. Each bulge forms a stiffening arch in the bolus and prevents buckling of the bolus at the corresponding ports.
In this embodiment, the dual lumen tube is a 13.5 French tube, giving it a nominal O.D. of 0.180 inches. The bolus, on the other hand, is 10 French size, i.e., it has a nominal O.D. of 0.136 inches. The catheter tip tapers from the 13.5 French size to the 10 French size between the second and third ports. As such, the inflow lumen has a D-shape until it reaches a tapered middle of the bolus, whereupon it transitions to a circular cross-section. At the same time the cross-sectional area of the lumen increases from 0.005 in2 to 0.006 in2.
In a conventional dual lumen catheter, substantially the entire volume and pumping force of returning processed blood is directed primarily out of the end of the outflow lumen because of the orientation of the end port and the size and shape of any conventional side ports employed. Little processed blood actually flows out through side ports. The present invention allows higher outflow and inflow rates. The redirection of a portion of the outflow through side ports separated from the main port reduces the speed and force of the outflow from the main port. Fluid pressure is reduced before the outflow reaches the main port. This reduction in force results in better diffusion and protects against whipping and cell destruction. The intake port is positioned and configured to prevent clogging and occlusion due to xe2x80x9cvein wall sucking.xe2x80x9d In addition, both port configurations are smooth and without sharp edges whereby damage to blood cells is greatly reduced.